1. Field of the Invention
The present invention relates to an ignition coil for an internal combustion engine (hereinafter, referred to as an ignition coil for short).
2. Description of the Prior Art
A structure of an ignition coil for a motor vehicle is, for example, as described in Japanese Unexamined Patent Publication No. 11-111545, constituted by a primary coil wound around a primary spool, a secondary coil wound around a secondary spool which are concentrically arranged in an outer peripheral side of a rod-like center core, a resin member (a potting member or a cast resin) charged into a gap between these plurality of parts, and the like.
However, since coefficients of linear expansion of the respective constituting parts are different from each other, a crack or the like may be generated between the constituting parts (particularly, in a root side of a collar portion in a spool around which a coil winding is arranged) due to a thermal stress. Further, each of the spools is frequently integrally formed by a resin, however, a flow of mold resin is deteriorated in some shapes thereof, so that a void or the like may be generated. Then, since the generation of the crack, the void or the like causes a dielectric breakdown by each of the spools, it is necessary to restrict and prevent them.